I did the water heater thing a few years ago. Probably long enough that by today's standards I will be doing it again sooner than I would like. I think the last one was around 2004 or so. By the date codes on it the guy said it had been in place since 1963. If I had been the original owner and got that kind of mileage out of it I would have been happy but no such luck, it came with the house and already had more than 30 years against it by the date given.